Cu proteins are involved in O2 binding, activation for hydroxylation and cofactorformation, the four electron reduction of O2 to H2Oand the two electron reduction of N2O to N2. These often exhibit unique spectroscopic features that reflect novel geometricand electronic structures that make major contributions to function. Research involves the application of a wide variety of spectroscopic and electronic structure methods to define the active sites in these proteins, related model complexes and their intermediates and determine geometric and electronic structure contributions to function. Specific aims~aTe: 1) Definition of the reaction coordinate of oxy-tyrosinase (Ty) and determination of differences in substrate interaction with the similar coupled binuclear copper sites in hemocyanin, Ty, mutants of Ty associated with oculocutaneous albinism, and catechol oxidase related to differences in function; 2) Definition of the coordinatively unsaturated nature of the trinuclear Cu cluster site in the multicopper oxidases (MCO's), its reaction coordinate for O2 reduction to H2O, its coupling with the Type 1 center as related to intramolecular electron transfer and its interaction with metal ion substrates relevant to iron metabolism and its genetic disorder aceruloplasminemia; 3) Extension of model studies to the active sites in dopaminelTmonooxygenase and peptidylglycine a-hydroxylating monooxygenase,involved in the control of neurotransmitters and peptidic hormone production, to determine the reaction coordinate for O2 activation by a single Cu center; 4) Definition of electronic^tructure/reactivity correlations for the u4-sulfide bridged tetranuclear Cuz cluster which catalyzesthe reduction of the green house gas N2O; 5) Determination of the nature of tyrosine residue activation by Cu sites in the O2 dependent biosynthesis of the organic cofactors in amine qxidase and galactose oxidase; 6) Definition of O2 intermediates in heme/Cu models of cytochrome c oxidase, the terminal enzyme in aerobic metabolism, to understand its reaction coordinate for O2 reduction relative to the MCO's and how this relates to proton pumping for ATP synthesis. Relevance: Cu proteins play crjticalvjx[unreadable]j<|s in Fe, Cu and 02 metabolism, are related to a range of genetic diseases, and are important in biotechnology, detoxification and the elimination of the green house gas nitrous oxide. Understanding Cu biochemistry on a molecular level provides mechanisms to improve or inhibit these processes and enhance drug design.